1. Field of the Invention
The present invention relates to a magnetic recording and reproducing method for recording and reproducing signals by helical scan with a double azimuth head arrangement in such devices as 8-mm VTR's (video tape recorders) and R-DAT's (digital audio tape recorders).
2. Description of the Prior Art
With magnetic recording systems that use magnetic tapes as their recording medium, the so-called helical scan method is gradually replacing the conventional longitudinal recording method whereby signals are recorded by a fixed head onto the magnetic tape in its longitudinal direction. The helical scan method, designed to meet today's demand for recording in ever-higher density, involves recording signals obliquely relative to the longitudinal direction of the tape by use of a head attached to a rotating drum. The helical scan method is attracting attention for its potential application in business-use notebook-size recorders.
To attain higher recording density in a helical scan setup requires increasing the recording track density. That is, signals are to be recorded onto contiguous tracks that are as close to one other as possible. However, too narrow a pitch between recording tracks can eliminate what is known as the guard band between these contiguous tracks. This may cause the head to pick up signals not only from the current track but also from the adjacent recording track. The phenomenon, called cross talk, hampers signal detection for high quality reproduction.
One prior art method proposed to prevent cross talk is as follows: two heads (A and B) are attached to the rotating drum. These heads are mounted so that they have a predetermined angle each relative to a reference line, one angle having the opposite polarity of the other (e.g., +.theta. and -.theta., a counterclockwise and a clockwise angle respectively relative to the reference line). Where signals are recorded by use of the rotating drum having the two heads A and B with different mounting angles, the two heads scan the tape alternately. The gap direction of the heads A and B (i.e., vector of the gap magnetic field) is inclined relative to the scanning direction thereof. The signals are recorded onto recording tracks at the azimuth angle formed by the two heads A and B.
With the signals thus recorded onto recording tracks at the azimuth angle of the two heads A and B, it is possible practically to prevent, during reproduction, one head from detecting the signal magnetic field from the recording track of the other head. The scheme is supposed to offer normally reproduced signals with no cross talk.
The helical scan-based systems use as their magnetic recording medium the so-called evaporated or coated type magnetic tapes. The evaporated tape is constituted by a base film, made illustratively of polyethylene terephtalate, coated with a magnetic layer. The magnetic layer comprises a metal or alloy magnetic substance (e.g., Co-Ni alloy) deposited direct onto the base film by plating or by known vacuum thin film forming techniques (e.g., vacuum evaporation, sputtering, ion plating). On the other hand, the coated magnetic tape is produced by applying a coating material on a base film, the coating material constituting the magnetic layer. The coating material is made from needle magnetic particles dispensed in a binder composed of an organic polymeric material. The needle magnetic particles include Co-clad gamma-ferrite magnetic particles or ferromagnetic particles (called metal magnetic particles) constituting a surface oxide layer.
A deficiency has been experienced where signals are recorded to and reproduced from the above recording medium by helical scan with the double azimuth head. That is, there occurs a difference in reproduced output between the heads A and B, causing the picture quality and other characteristics to deteriorate. This is attributable to the gap direction of one head being different from that of the other head relative to the longitudinal direction of the tape in which magnetic particles are generally oriented; the particles constitute the magnetic layer of the recording medium.
The cross talk phenomenon is prevented effectively by enlarging the difference in the gap direction tilt angle (i.e., azimuth angle) of each head relative to the longitudinal recording tracks on the tape. However, the greater the difference in azimuth angle, the greater the gap direction difference between the heads A and B relative to the direction in which the magnetic particles are oriented. This leads to further deterioration of characteristics.